What are your favorite OS X features?

My all time favorite thing is the amazing multitouch trackpad gesture support. A lot of my PC-toting friends struggle to do 2 finger gestures on their trackpads and I can do 4-5 finger gestures without any trouble. I also like the fullscreen apps since it meant I didn't have to pony up more money for a 15" MacBook Pro. Mission Control is also an amazing multitasking tool for me. Of course, all of these are also supercharged by the multitouch gestures.

So what are your favorite features in OS X?